1. Field of the Invention
The present invention relates to a process for preparing molded flexible polyurethane foam and to the molded foam prepared thereby. More particularly, the invention relates to molded flexible polyurethane foam employing urea-biuret modified polyisocyanates.
2. Description of the Prior Art
U.S. Pat. No. 3,526,652 teaches the preparation of urea-biuret containing polyisocyanates by treating polyphenylene polymethylene polyisocyanate with about 0.1 percent to about 0.5 percent water at temperatures from about 100.degree. C. to about 140.degree. C. U.S. Pat. No. 3,936,483 teaches the use of a polyisocyanate mixture comprising from about 10 percent to about 90 percent toluene diisocyanate and the balance a mixture of polyphenylene polymethylene polyisocyanates. U.S. Pat. No. 4,221,877 teaches the preparation of biuret modified diphenylmethane diisocyanate by reacting from about 0.1 equivalent of water to about 0.3 equivalent of water per equivalent of diisocyanate. The prior art does not teach that molded flexible polyurethane foam with improved air flow and compression set may be prepared from a mixture of urea-biuret modified polyisocyanates.